Case Study

A Project Manager's Nightmare

So your company just bought a set of tanks from another oil company.... Unfortunately, they each have approximately 7,000 barrels of highly paraffinic/asphaltenic sludge accumulated over more than twenty years.

But it=s not a big dealCyou have several months before marketing needs the tanks.

Surprise!A change of plan, marketing needs to have the tanks ready for product service in less than two months. The tanks must be cleaned, repaired and made ready for new service. What a nightmareBoften removing the sludge could take the time available. But wait, it gets worse! The tanks were filled to above-manway levels, making their removal very risky. Hot taps and door sheets were out of the question Further, the material was too viscous to pump down to a safe level for removal. Technically speaking, the sludge had the following characteristics:



Paraffin Content


Water Content


Asphaltene Content


Inorganic Residues


Quad was able to help in just such a situation. We combined chemistry specifically formulated to disperse the constituents of the sludge and inhibit their reformation, diluent provided by the customer and specifically designed hydraulic circulation equipment to liquefy the sludge (and keep it liquid at ambient temperature). We then removed it from the two tanks, in preparation for recovery. All of the product was recovered inside the tank. The sludge material was fully recovered as a salable product and sent to a refinery for processing.

Total time for the initial project (the customer added a third tank, since the others had gone so well) was 46 days. Just down the way, another contractor was performing a similar job for another company, but they were using more conventional means. They started before Quad and finished much later. Most important, since they used more labor-intensive conventional means (dig it out then process it to recover hydrocarbons), the entire area was a mess, with hydrocarbon material everywhere. The Quad site looked like nothing had ever happened... no spills... no muss... no fuss.. much more professional.

Quad=s techniques offered the customer the flexibility to conduct other work necessary in readying the tanks for service. Mixers and valves were placed on the tanks and valves were removed, tested and replaced during Quads work. In addition new piping was installed and connected during our activities, In short Quad=s desludging work did not slow down the overall project, since its activities were conducted in parallel with other work.

When we completed our desludging, the material had the following characteristics:

API Gravity


Pour Point

-22O F

Cloud Point

-5O F

And what about the cost. B only half of what it would have been!

Simply the best technique for removing paraffinic and asphaltenic crude sludges from storage tanks, Quad=s approach offers numerous advantages over conventional removal and processing methods.


Quads approach...First understand the nature of the material to be dealt with and the customer=s objective. Once analyzed for content, we next determine the best diluent material to be used to recover the sludge (this is arrived at by exploring the technical options and reviewing these with the customer to determine the most economically available material (a trade-off often occurs depending upon the effectiveness of a certain diluent-or the amount it will take per unit of sludge, verses its unit cost). We then optimize the chemical assistance program to ensure not only liquefaction of the recovered material, but also the stability of it.

Sludge is a general term used to describe the residual deposit found at the bottom of tanks and other storage vessels. Sludge deposits are commonly found in vessels handling raw crude oil, or processed oil. The physical nature of sludge varies, but in general they are usually a viscous semi-solid, composed of a mixture of water, light hydrocarbons, waxes, asphaltenes and sometimes inorganic solids such as sand, iron sulfides and iron oxides.

Sludges form when a crude oil=s properties are changed, due to changes in external conditions. Cooling below the cloud point, mixing with incompatible materials, and the introduction of water to form emulsions, make up the more common caused for sludge formation. The precipitate that forms is often enriched in the second phase materials-waxes, water, solids, and asphaltenes.

Selection of the proper diluent or solvent material can be critical. Selection of the wrong material can not only be costly, it can lead to opposite of the desired results. For example asphaltic materials in mixed sludge containing asphaltenes co-precipitated with waxes are often close to the formation of insoluble particles. Introduction of the wrong solvent can solubilize the wax, resulting in a precipitation of hard insoluble asphaltenes. Quad selects the solvent or solvents which are compatible with the sludge and minimizes the precipitation of solids.

Quad utilizes several chemical systems to recover and stabilize the recovered crude materials. Several mechanisms of action are generally brought to bear.

The viscosity of a mixture is often due to the presence of an internal phase, which may formed of waxes in an interconnecting matrix, making the sludge thixotropic ( high viscosity at low shear and low viscosity at high shear). Generally the sludge exhibits a hysterisis (its properties will change with its shear history). Shear can often break the weaker electrostatic bonds, but it must often be very high, and given time (often short) the bonds will re-form and sludge will re-accumulate.

Certain chemical systems can act to change the electrostatic charge on the wax crystals, acting as an electrostatic wedge prying the crystals apart, eliminating the thixotropic properties, minimizing the reformation of sludge and wetting the material making them more soluble in the recovery diluent or solvent.

In addition to acting on existing particles to Abreak them down@ for recovery, Quad adds chemicals which act on particles to inhibit their growth and to change their thermodynamic properties, effecting the way the particles act under changing temperature conditions.

Certain chemical systems combined with carefully selected solvents can make the removal and recovery of sludges simple. These chemicals act to reduce the amount of energy and time required over conventional techniques, by changing the thixotropic nature of many sludges and can further enhance recovery by decreasing the probability that the sludge will reform or by extending the ability of the solvent to dissolve the previously precipitated materials.

Once solvent and chemical system options are found, Quad measures the economic trade-off associated with each, especially considering the customer=s available solvent resources and costs. Then the best solution can be suggested.

Finally, Quad designs the best system of delivery of the solvent/chemical system. Quad=s techniques focus on minimization or elimination of personnel and environmental exposure. A combination of hydraulic circulation and injection equipment, custom specified for the particular application is used to achieve mixture of the materials.

Once Quad has completed its work, the material has been converted to good quality usable material, typically used for fuel or for refining feed stock, among others. This is a dramatic conversion from material which would otherwise be waste.


Call us : 713-477-6460   Fax us: 713-477-7454      E-mail us: Chuck Goodner chuck,goodner@quadenviroservice.com , Fred Sieber sieberfa@quadenviroservice.com or Steve Ohm steve.ohm@quadenviroservice.com
Last modified: July 26, 2005